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Message-ID: <3D7D7273.94F6387D@azglobal.com>
From: Richard
X-Mailer: Mozilla 4.76 [en] (WinNT; U)
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Newsgroups: alt.binaries.schematics.electronic,sci.electronics.design,sci.electronics.misc,comp.dcom.telecom.tech
Subject: Re: Cable Modem Question
References: <96tnnu8l9bjqh73sgusubbm7al06g80prh@4ax.com>
Date: Tue, 10 Sep 2002 04:17:26 GMT
NNTP-Posting-Host: 68.2.65.245
NNTP-Posting-Date: Tue, 10 Sep 2002 00:17:26 EDT
Organization: Cox Communications
mike wrote:
> [...] a friend claims to get 800kbps up and down.
Performance is very conditional on the provider, their backbone &
peering, the site you're going to, and... the cable modem settings they
configure. You may see numbers better or worse than your friend.
> Is there error correction in the physical layer
> or is that still done furthur up the TCP/IP stack?
Yes and yes. The carrier can optionally enable "forward error
correction" (FEC) in the cable modem channel - this can fix damaged
packets, but does not retransmit them. If packets are unrecoverable,
then it's up to TCP to retransmit the missing packet.
> The 2.560 Msym up is shared by all the customers
> on the node, correct? So my friends slice is
> 800kbps.
Yes, it's shared. No, he doesn't have a dedicated 800Kbps "slice".
Performance depends on the channel he happens to be on at the moment,
how many others are active on it, what the channel's settings are
(encoding, FEC, symbol rate, etc.). These can all change over the
course of a day.